1. Field of the Invention
The present invention relates to systems and methods for providing a plurality of antennas using a single core and, in particular embodiments, to systems and methods for providing an implantable device having multiple antennas and a single core that is inductively coupled to an external unit.
2. Description of Related Art
The ability to inductively couple radio signals between two or more coils has greatly facilitated the use of implantable devices in patients who require internal monitoring, sensing or regulation of various physical parameters or who require internal delivery of a drug or medication. RF communication between an implant unit and an external device has allowed many such patients to receive effective medical treatment and/or analysis while maintaining mobility realizing the mobility and other benefits of an implanted device.
For example, for patients requiring automatic pacing of the heart, implantable pacing devices can record electrical activity in the heart and the response of the heart to pacing signals. The recorded information can then be transmitted via inductive coupling of RF signals to a receiving unit external to the patient and be analyzed and evaluated by an attending physician. The ability to inductively couple data via RF transmission eliminates the need for costly and burdensome invasive surgery to recover recorded data in the implant unit.
In a similar manner, many diabetic patients utilize implantable pumps and insulin delivery systems for the regulated delivery of insulin to their bodies. These patients can also transmit recorded data relating to the delivery of insulin and the corresponding response by the body to an external unit where the data can be analyzed. In response to the analysis, the parameters of the insulin delivery system may be adjusted by inductive coupling of an RF signal from an external unit to the implant unit. No invasive surgery to reach the implant unit is necessary.
Inductively coupled implant units to date, however, have not given patients complete freedom from external monitoring or control devices. The quasi-static magnetic filed produced by a coil is highly directional in nature and the link between a coil in an implant unit and a coil in an external unit depends on the relative orientation between transmitter and receiver coil antennas. To ensure a reliable link independent of transmitter and receiver orientation, the ability to generate or receive a modulated magnetic field in more than one direction is required, which, in turn, requires the use of multiple antenna coils.
In past designs having multi-directional magnetic field performance, separate antennas, each having its own air or ferrite core, have been used for multi-directional magnetic field transmission and reception. A design of this type may be seen in FIG. 1. In FIG. 1, an implantable circuit 10 includes having integrated circuits 18 includes three separate antennas 12, 14 and 16, one for each axis in three-dimensional space and each antenna having its own core. For effective multi-directional operation, at least one of the antennas 12, 14 and 16 must be oriented in a plane perpendicular to two of the antennas, as shown in FIG. 1. This type of configuration greatly increases the space required to house the system. Since space in an implantable unit is critical and always at a premium, the space required by this type of three-antenna system is relatively large and, thus, is a drawback for patients who are outfitted with an implant unit utilizing this type of system.
Because of the space issues associated with a design of the type shown in FIG. 1, other past designs have incorporated only a single antenna for data transmission/reception. Single antenna designs generate a highly directional magnetic field. For operation, a patient having a single antenna implant device has had to position an external unit directly adjacent to the implant device and in align the antenna of the external device with the antenna of the implant unit to effect transmission or reception. Systems of this type have mobility limitations, rendering the patient stationary while trying to transmit or receive data. In addition, because of the directional nature of the a single antenna device, and the inability of the patient to ascertain the exact orientation of the implanted antenna, maximum data transfer rates and accuracy may be diminished in a single antenna system.